1. Field of the Invention
This invention relates to a composite material consisting of an insulating substrate of single crystal diamond and cubic boron nitride epitaxially grown thereon.
2. Description of the Prior Art
It is generally known that cubic boron nitride (hereinafter referred to as "cBN") has the largest band gap (6 to 7 eV) as a semiconductor material and both P type and N type semiconductor can be prepared therefrom by adding impurities. Thus, it has eagerly been desired to develop the cBN semiconductors for the device operated at a high temperature or ultraviolet semiconductor laser device.
When a crystal is grown, in general, the growing is carried out on a substrate and as a substrate for the growth of cBN single crystal, there has hitherto been used only cBN itself. However, cBN having such a size and quality as to be suitable for use as a substrate has not been obtained up to the present time. Therefore, a good single crystal substrate as a substitute for cBN itself is essential considering the above described application and development of cBN as a semiconductor material.
As a substrate material for the growth of cBN, diamond having a lattice mismatch with cBN of only about 1.3% and substantially equal thermal expansion coefficient has been taken into consideration and up to the present time, a hetero junction of diamond and cBN has been proposed, for example, by W. E. Picket, Phys. Rev. B. vol. 38, 1316, 1988.
However, no report has been made on the growth of cBN on diamond as a substrate There has been no such precedent as succeeding in the growth of cBN on the heterogeneous substrate. That is, when considering the application of cBN to semiconductor devices operated at high temperatures, semiconductor optical devices capable of emitting ultraviolet rays, etc., which have hitherto not been prepared, there arises a problem that there is no suitable substrate for the growth of cBN.